Discharge hysteresis in motoneurons (Powers & Heckman 2015)

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Accession:183949
"Motoneuron activity is strongly influenced by the activation of persistent inward currents (PICs) mediated by voltage-gated sodium and calcium channels. ... It has recently been suggested that a number of factors other than PIC can contribute to delta F (firing rate differences between motoneurons) values, including mechanisms underlying spike frequency adaptation and spike threshold accommodation. In the present study, we used a set of compartmental models representing a sample of 20 motoneurons with a range of thresholds to investigate how several different intrinsic motoneuron properties can potentially contribute to variations in F values. ... Our results indicate that, although other factors can contribute, variations in discharge hysteresis and delta F values primarily reflect the contribution of dendritic PICs to motoneuron activation.
Reference:
1 . Powers RK, Heckman CJ (2015) Contribution of intrinsic motoneuron properties to discharge hysteresis and its estimation based on paired motor unit recordings. A simulation study. J Neurophysiol 114:184-198 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): Spinal cord L motor neuron alpha;
Channel(s): I Na,p; I Na,t; I L high threshold; I K; I M; I K,Ca; I_AHP; I Calcium; I Sodium;
Gap Junctions:
Receptor(s):
Gene(s): Kv1.2 KCNA2; Kv1.9 Kv7.1 KCNQ1;
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Spike Frequency Adaptation;
Implementer(s): Powers, Randy [rkpowers at u.washington.edu];
Search NeuronDB for information about:  Spinal cord L motor neuron alpha; I Na,p; I Na,t; I L high threshold; I K; I M; I K,Ca; I Sodium; I Calcium; I_AHP;
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Discharge_hysteresis
Model hoc files and output
README.txt
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gramp.ses
HiDKCa.csv
init_3dend_gramp.hoc
LCai.csv
Napi.csv
pars2manyhocs.py *
ProxCa.csv
SetConductances2.hoc *
SlowM.csv
standard.csv
twobirampsdel.hoc *
                            
 COMMENT
 
 kca2.mod
 
 Calcium-dependent potassium channel
 Based on
 Pennefather (1990) -- sympathetic ganglion cells
 taken from
 Reuveni et al (1993) -- neocortical cells
 
 Author: Zach Mainen, Salk Institute, 1995, zach@salk.edu
 modified Jan,2000 by RKP;modified July 2005 to include a contribution from calcium
flowing through L channels
 	
 ENDCOMMENT

 NEURON {
 	SUFFIX kca2
 	USEION k READ ek WRITE ik
 	USEION ca READ ica WRITE cai
  USEION caL READ icaL 	
  RANGE n, g,ik,cai,ica,icaL,depth1,taur1,depth2,taur2
 	GLOBAL Ra, Rb, caix
 }
 
 UNITS {
 	(mA) = (milliamp)
 	(mV) = (millivolt)
 	(S) = (siemens)
 	(um) = (micron)
 	(molar) = (1/liter)			: moles do not appear in units
 	(mM)	= (millimolar)
 	(msM)	= (ms mM)
 	FARADAY = (faraday) (coulomb)
 } 
 
 PARAMETER {
 	g = 0.03   	(S/cm2)	
 	v 		(mV)
 	cai  		(mM)
 	caix = 2	
  cainf=0.0001
 	depth1	= .1	(um)		: depth of shell
 	taur1	= 20	(ms)		: rate of calcium removal
 	depth2	= 10	(um)		: depth of shell
 	taur2	= 200	(ms)		: rate of calcium removal
								
  Ra   = 0.1		: max act rate  
 	Rb   = 0.1		: max deact rate 
 
 	celsius		(degC)
 } 
 
 
 ASSIGNED {
 	ik 		(mA/cm2)
	 ica (mA/cm2)
 	icaL (mA/cm2)
 	ek		(mV)
 	ninf
 	ntau 		(ms)	
  drive_channel1	(mM/ms)
  drive_channel2	(mM/ms)
 }
  
 
 STATE { 
 n 
 ca (mM)
	caL (mM)
}
 
 INITIAL { 
	ca=cainf
 caL=0
 cai=cainf
 rates(cai)
 	n = ninf
 }
 
 BREAKPOINT {
         SOLVE states METHOD cnexp
 	ik =  g *n* (v - ek)
 } 
 

DERIVATIVE states {  
 	drive_channel1 =  - (10000) * ica/ (2 * FARADAY * depth1)
 	if (drive_channel1 <= 0.) { drive_channel1 = 0. }	: cannot pump inward
 	ca' = drive_channel1 + (cainf-ca)/taur1
 	drive_channel2 =  - (10000) * icaL/ (2 * FARADAY * depth2)
 	if (drive_channel2 <= 0.) { drive_channel2 = 0. }	: cannot pump inward
 	caL' = drive_channel2 + (cainf-caL)/taur2
 	cai = ca + caL

          rates(cai)    
         n' = (ninf-n)/ntau
}
PROCEDURE rates(cai(mM)) {  LOCAL a,b
							UNITSOFF
         a = Ra * (1e3*(cai  -cainf))^caix		: rate constant depends on cai in uM
         b = Rb
         ntau = 1/(a+b)
        	ninf = a*ntau
					UNITSON
 }

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